FIG. 1 (Prior Art) illustrates a radio network congestion and a core network congestion use case in an LTE network 100. LTE network 100 comprises an application server 110, a packet data network gateway (PDN GW) 120, a serving GW 130, two base stations eNB141 and eNB142, and a plurality of user equipments (UEs). Radio network congestion occurs when massive concurrent data transmission takes place in the radio access network, as depicted by arrow 151. On the other hand, data congestion may occur in the mobile core network or on the link between the mobile core network and the application server 110 where the data traffic related to the application is aggregated, as depicted by arrow 152.
Modern networks use congestion control and congestion avoidance techniques to try to avoid network congestion. LTE has specified several barring mechanisms for concurrent congestion control. Access Class Barring (ACB) is a mechanism to limit the number of simultaneous access attempts from certain UEs. All UEs are member of one out of ten randomly allocated mobile populations, defined as access class 0 to 9. The population number is stored in UE's SIM/USIM. In addition, the UEs may be members of one or more out of five special categories (e.g., Access Class 11 to 15), also stored in the SIM/USIM. Under the ACB mechanism, the network operator may prevent certain UEs from making access attempts or responding to pages in specific areas of a PLMN based on the corresponding access class. Enhanced access barring (EAB) is an enhanced access barring mechanism to avoid Machine Type Communication (MTC) overload. Service Specific Access Control (SSAC) is used to apply independent access control for telephony services such as IP Multimedia Subsystem multimedia telephony (MMTEL) services.
FIG. 2 (Prior Art) illustrates various barring mechanisms for congestion control in an LTE system 200. LTE specifies several barring mechanisms for concurrent congestion control in different layers. In non-access stratum (NAS) layer, for RRC Idle mode, LTE specifies Service Specific Access Control (SSAC) for MMTEL services and EAB for MTC devices. For RRC Connected mode, SSAC may be applied. In Access stratum (AS) layer, for RRC Idle mode, ACB is in general applicable to all types of services and devices. For RRC Connected mode, random access backoff, RRC reject/release, and scheduling request (SR) masking can be used as well.
Some of the barring mechanisms in LTE, however, have duplicate behavior and therefore may cause quality degradation in some scenarios. For example, double barring of SSAC and ACB for MMTEL service de-prioritizes MMTEL service and LTE fails to prioritize MMTEL service over other services. Furthermore, congestion control for RRC Connected UEs becomes more important as the trend is to keep UE in RRC Connected for data applications. However, LTE lacks congestion control mechanism for RRC Connected mode. Therefore, it is desirable to provide a feasible congestion control mechanism with a fine granularity that can prioritize or deprioritize services based on operator's requirement. In addition, the congestion control mechanism can be applied for RRC Connected mode as well with proper granularity.